The descending noradrenergic bulbospinal pathway effects on transmission of sensory information by dorsal horn cells is being studied. Preliminary work has shown that this system, following activation by intravenous L-DOPA, causes an increase in dorsal horn cell responses to cutaneous mechanical stimuli. The current project will determine the effects of intravenously injected L-DOPA on transmission of noxious sensory information by single dorsal horn cells. The animals will be depleted of serotonin prior to the acute experiment because of the previously demonstrated release of serotonin by L-DOPA. In addition the pharmacologic characteristics of the L-DOPA effects will be studied. It will be determined if the L-DOPA effects can be blocked by treatment with: a) dopamine-beta-hydroxylose inhibitors; b) alpha adrenergic blockers; c) beta-adrenergic blockers; d) destruction of descending bulbospinal noradrenergic terminals with intracisternal 6-hydroxy-dopamine. These maneuvers will determine if, in fact, L-DOPA modulation of sensory transmission is due to overflow of noradrenalin from descending bulbospinal terminals. The origins of the descending noradrenergic pathways, including locus ceruleus, the A1 and A2 portions of the medulla will be stimulated in attempts to duplicate the effects found following L-DOPA injection.